Data processing equipment often utilizes magnetic disks as the information storage medium. In such equipment, the information is stored on magnetic surfaces of the disk which is rotated at a high speed in an enclosure with access to the magnetic surfaces by way of a plurality of read/write transducer heads that generally move radially in relation to the disk surfaces. To achieve maximum magnetic coupling between the magnetic surfaces and the transducer heads, the transducer heads are positioned extremely close to the surfaces of the disk and, in fact, each "files" on an air cushion a few tenths of microinches off the surfaces of the magnetic disk. The magnetic disk enclosure is a closed system and is generally assembled in a clean room to exclude foreign particles from the interior of the enclosure to the greatest possible extent. However, some contaminant particles are generally still present in the assembly room and these contaminant particles may find their way into the enclosure. Other particles may be generated by the rubbing action of heads and disk surfaces during starting and stopping. With the disk rotating at a minimum of 1500 revolutions per minute, the heads "flying" close to the disk surfaces, and high recording densities of 100 tracks per inch and an excess of 1000 bits per inch, microscopic particles, although invisible to the naked eye, may disturb the flight of the heads and cause damaging collisions between the heads and the disk surfaces which may cause scratching of the disk surfaces and destroy, or at least substantially impair, the operability of the system.
Various means have been investigated to remove contaminant particles from the surfaces of a magnetic disk. One prior art technique is to move a flexible comb or brush lightly across a surface of the disk after the disk has been brought up to operating speed. The fibers can sweep the particles off the disk or merely dislodge the particles from the disk so that the particles are thrown off the disk by centrifugal force or carried off by the viscious drag force of the air flow directed radially across the surface of the disk. In addition, air may be forced by a fan across the surface of the disk to further aid in removing dislodged particles from the disk surface.
In another type of contaminant particle trapping system, a rotating magnetic disk is used to set up areas of different static pressures of the fluid (air) within the disk enclosure, with a first area having a first static pressure and a second area having a second static pressure less than the first static pressure by an amount sufficient to carry particles in the fluid from the first area to the second area through an external conduit. The conduit contains an absolute filter which collects all particles over a selected size, for example, all particles over 20 microinches.
Neither of the methods described adequately remove contaminant particles from the disk enclosure. In the method where the contaminant particles are merely loosened, or flung off the disk surface by centrifugal force, the contaminant particles are not permanently captured but are allowed to circulate in the air within the enclosure. Due to the close spacing between the transducer heads and the disk surfaces, the air borne particles can find their way between the transducer heads and the disk surfaces with resulting interference with the read/write operation and possibly permanent scratching of a disk surface. Also, since the contaminant particles are not permanently captured, the particles will settle on the disk surface when the disk stops rotating, necessitating further brushing of the disk surface when the disk is again used. Also, the brushing may continue for a relatively long period, for example about 20 seconds, thereby causing a serious loss of operating time when disks are changed often. In the method where the rotating disk creates a pressure differential to force contaminant particles through a filter, it is difficult to maintain an air flow through the filter due to the large back pressure developed when the filter is an absolute filter designed to remove all particles over 20 microinches in diameter.